Driver for variable resistors



Oct. 11. 1949. M. B. ARISMAN ETAL DRIVER FOR VARIABLE RESISTORS Filed March 17, 1949 v Ralph KCMdgnL/sm Patented Oct. 11, 1949 narvnn FOB vaamnnn ansrs'roas Mervin B. Arlsman, W. Magnusen,

Incl,

Adrian J. Vaksvik, and Ralph Elkhart, Ind., assignors to Chicago Telephone Supply a corporation of Indiana Corporation, Elkhart,

Application March 17, 1949, Serial No. 81,872

1 Claims.

This invention relates to electrical control devices and refers particularly to variable resistance controls of the type used in radio and television apparatus. The invention is advantageous in situations where two control devices are connected in tandem with the shaft of one hollow and having the shaft of the other rotatable therein.

In such controls rotation of the shaft sweeps a contactor across the face of a resistance element and to assure good electrical contact the contactor generally comprises spring fingers maintained under tension. To place and maintain these spring fingers under tension entails supporting the control shaft and, in fact, the entire rotating assembly of the control, against inward or rearward thrust.

In conventional controls of this type the shaft has an annular groove in line with the front end of the bushing through which the shaft protrudes and a C washer is seated into this groove to bear against the front end of the bushing and thus hold the shaft against rearward axial displacement. In the case of tandem controls where one control shaft operates within theother, this manner of holding the rotatable unit driven by the hollow control shaft against rearward axial displacement cannot be used since the hollow,

shaft does not have suflicient wall thickness to permit an annular groove to be cut therein. This is especially so in the very small controls recently developed for radio and television.

Consequently it has been the practice in the pastto have the inner end of the hollow control shaft bear against the inner face of the cover of its control unit or against a hat-shaped washer supported thereon. However, the way in which the inner or rear end of the control shaft was secured to the driver which carries the"contactor always involved ears struck from the shaft and bent over the rear face of the driver so that these cars constituted the rearmost portion of the rotatable assembly and perforce were the parts thereof which bore against and rode on the cover wall or washer Supported thereon. This construction lacked the desired smoothness. Not only was the surface against which the ears bore inherently rough but since the ears were struck from portions of a tube they were arcuate in cross section, even after they were bent over.

Precautions were taken to flatten the ears as much as possible but notwithstanding, the faces of the bent-over ears inevitably possessed a degree of concavity so that the actual contact with the wall of the cover was by the relatively sharp side edges of the ears.

Moreover, since the ears of necessity were relatively narrow, the thrust bearing formed by thev tact over a substantial area with the inner face a of the cover wall.

Another object of this invention is to provide a driver for variable resistors which incorporates within itself the carrier for the contactor, a smooth annular thrust bearing surface, and rotation limiting stop abutments.

Still another object of this invention is to provide more accurate positioning of the contactor with respect to the resistance element than was possible with the previous built-up construction of the contactor-driver assembly in which the contactor was mounted on an insulated drive arm which in turn' was fixed to a stamped metal arm secured tothe shaft and termed the stop arm since it carried the stops for limiting rotation of the shaft. With this built-up constructionthe positioning of the contactor, and hence the magnitude of the contact pressure and to a large degree the smoothness of operation was affected by several possible variables. The possible variations in the thickness of the insulated drive arm, the metal stop arm and the hat shaped thrust washer upon which the fastening ears rode, as well as the inevitable variations in the flatness of the ears and any possible variations in the thickness thereof all had an important bearing upon the accuracy of the positioning of the contactor. V

The present invention eliminates these many With the above and other objects in viewwhich will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawing illustrates one complete example of the physical embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a side view of a dual tandem variable resistance contro. embodying this invention, parts thereof being broken away and in section;

Figure 2 is a perspective view of the driver of the front unit which has the hollow shaft, and the adjacent inner end of its shaft shown disassembled;

Figure 3 is a perspective view of the cup-shaped cover for this front unit showing its flat inner face against which the annular runner of the driver abuts when the parts are assembled; and

Figure 4 is a mrspective view of the assembled driver and shaft and illustrating the same from the front thereof to show' the manner in which the contactor is mounted on the driver.

Referring now particularly to the accompanying drawing, the numerals 5 and i designate the two units of a dual or tandem control of the type to which this invention pertains. In use both units are mounted on the supporting panel (not shown) by means of a single mounting sleeve 1. Each of the two units comprises a base 8 having an arcuate resistance strip 9 and a collector ring it mounted on the inner face thereof. The usual terminals extend from the ends of the resistance strip and the collector ring.

A contactor indicated generally by the numeral H overlies the inner face of the base to be advanced along the resistance strip to effect the desired control function by rotation of a shaft journaled in the base. Spring contact fingers l2 and I 3 on the contactor, respectively, bear against the resistance strip and the collector ring ll. As will be readily apparent the tension under which these spring contact fingers are maintained in the assembled condition of the control unit imparts a rearward or inward thrust to the .contactor rotating assembly which, of course, must be opposed to retain the structure operatively assembled.

In the case of the rearmost control device 5 this requirement presents no serious problem since its rotating element is driven by a solid shaft l4 being solid, an annular C washer receiving groove l5 can be cut into the shaft adjacent to the outer face of the base 8 or a spacing plate I overlying the same without oblectionably weakening the shaft. An ordinary C washer l1 engaged in this groove bears against the spacing plate it to hold the shaft l4 and the parts mounted thereon against inward axial displacement.

In the case of the front control 6, however, other means must be provided to carry the inward thrust since its shaft ll, being hollow to rotatably receive the solid shaft, does not have sufficient wall thickness to permit cutting a C washer groove into it.

As noted hereinbefore, it was the practice in the past to utilize the end wall I! of the cupshaped cover 20 with which all control devices of this character are equipped to take the end thrust directly from the tubular shaft II, the actual bearing being between outstruck ears on the end of the shaft by which the contactor driver was held to the shaft and the inner face of the wall I! or a hat-shaped washer overlying the same. This past construction precluded the attainment and maintenance of the smooth operation necessary in controls of this -kind. Even though special precautions were taken to flatten down the ears some degree of concavity inevitably remained and the resulting sharp side edges had a tendency to bite into the metal surface upon which the ears rode.

The present invention overcomes this objectionable characteristic of past constructions by obviating the exposed attaching ears through the substitution of a molded one piece contactor driver 2| for the built-up construction heretofore used. Though bent-over cars 22 are used to mount the driver 2| on the tubular shaft I8, the ears are set down into a central round recess 23 in the rear face of the driver. The ears 22 are the endmost portions of diametrically opposite lugs 24 which project from the shaft l8 and are seated in notches 25 in the wall of a hole 26 axially through the driver. The hole 26 has substantially the same diameter as the bore of the hollow shaft ll so as to form a continuation thereof for the smooth reception of the solid shaft H.

Since the recess 23 is deeper than the thickness of the ears the edge of the wall defining the sides of the recess constitutes the rearmost portion of the driver and provides an annular runner 21 which lies in a plane normal to the shaft axis and rides directly on the inner face of the cover wall I.

Being relatively large in diameter, this annular runner provides a large bearing for the molded driver and since the tubular shaft is rigidly secured thereto this large bearing firmly holds the entire rotating unit against wobbling.

In addition to carrying the contactor and providing the rotating element of the thrust bearing, the molded driver 2| also serves the function of the stop plate of past constructions and to this end has 9. lug 2i integrally formed on its rear face. The sides of this lug provide abutments which coact with a stationary abutment formed by an instruck portion II on the cover 20 to limit rotation of the shaft.

From the foregoing description taken in con-- nection with the accompanying drawing it will be readily apparent to those skilled in the art that this invention assures smooth operation in controls of the character described since the annular runner 21 can ride smoothly across the face of the cover wall l9, and in all positions of rotation holds the rotating elements firmly against wobbling, and that since the driver (of which the runner 21 is a part) is a molding, the contactor always will be properly and accurately positioned with respect to the resistance element.

n will also be evident that while the invention is especially valuable'in the case of tandem controls where one of the shafts of necessity is a hollow tube of relatively small wall thickness, it

is equally susceptible to use in controls which have solid shafts.

What we claim as our invention is:

1. In an electrical control device having a base provided with a resistance element and a bushing, and having a cup-shaped cover attached to the base and coacting therewith to. provide a housing: a shaft journaled in the bushing and projecting into the housing; a driver flxed to the shaft at the end thereof inside the housing, said driver having an annular rearward projection concentric to the shaft with the extreme rear edge of said projection lying in aplane normal to the shaft axis and beyond the adjacent end of the shaft so as to provide a smooth uninterrupted runner adapted to ride on and receive support from the bottom wall of the cup-shaped cover, whereby said runner and the bottom wall of the cup-shaped cover constitute a thrust bearing; and a contactor carried by the driver and interposed between the base and the driver, said contactor having spring contact fingers to resiliently bear against the resistance element and by the spring tension thereof hold the circular runner against the bottom of the cup-shaped cover.

2. In an electrical control, the combination with a base having a bearing and an annular resistance element concentric therewith and exposed on the inner face of the base, and a cupshaped cover attached to the base and coacting therewith to provide a housing enclosing said resistance element, of: a shaft journaled in the bearing and projecting into the housing; a driver fixed to the shaft at the end thereof inside the housing; a contactor carried by the driver and having a spring contact finger to ride upon and resiliently bear against the resistance element; and an annular runner integral with the driver and extending rearwardly therefrom, said runner being concentric to the control shaft and its rearmost edge lying in a plane normal to the shaft axis and beyond the adjacent end of the shaft to ride upon and be supported by the inner contactor mounted on the driver and engaging the resistance element, the tension of the spring contactor imparting a rearward thrust to the driver and shaft; a cup-shaped cover positioned .over the rear face of the base and coacting with face of the cup-shaped cover whereby said anthe shaft and driver against inward displacement from a position maintaining the spring contact finger under tension.

3. An electrical control of the type having cooperating rotatable and stationary elements enclosed within a housing with the rotatable element movable by means of a shaft protruding from one wall of the housing, characterized by the provision of a thrust bearing comprising, the wall of the housing opposite that through which the shaft protrudes; and a part on the shaft hearing against said rear wall, the part on the shaft which engages the rear wall being a smooth annular runner concentric to the shaft axis with its rearmost edge lying in a plane perpendicular to said shaft axis and extending beyond the rearmost portion of the shaft so as to have a smooth running bearing upon the rear wall of the housing.

4. The electrical control set forth in claim 3 further characterized by the fact thatsaid part on the shaft is a one piece molding of insulati material. I

5. In an electrical resistance device: a base having a hole therethrough for the reception of the base to define a housing for the resistance element and contactor; and a thrust bearing to opposethe rearward thrust engendered upon the shaft and driver by the tension of the spring contactor, said thrust bearing comprising, a ring integral with the driver and projecting rearwardly therefrom beyond the rearmost portion of the shaft, the rear edge of said ring lying on a plane normal to the shaft axis and having a smooth sliding engagement with the adjacent end wall of the cup-shaped cover.

6. The electrical resistance device of claim 5 further characterized by the provision of cooperating stop abutments on the driver and the cup-shaped cover to define the limits of rotation of the rotatable elements of the control.

'7. In a variable resistance device of the type in which a resistance element is traversed by a contactor driven by a rotatable control shaft passing through a hole in a base of insulating material, and wherein the control shaft is biased endwise toward-the rear of the device: a cover attached to the base over the rear face thereof, said cover coacting with the base to form a housing for the device and having a wall substantially normal to the shaft axis and opposite the rear further characterized by the provision of cooperating stop abutments on the driver and the cover for limiting rotation of the driver and consequently the contactor.

9. In a variable resistance device of the typ in which a resistance element is traversed bya' contactor driven by a rotatable control shaft passing through a hole in a base of insulating material, and wherein the control shaft is biased end- .wise toward the rear of the device: a cover attached to the base and disposed over the rear face thereof, said cover having an endwall substantially normal to the shaft axis and-inline with the rear end of the shaft; a driver for the contactor fixed to the shaft and situated within the housing formed jointly by the cover and the base, said driver being a molding of insulating material and having a recess in its rear face, the side wall of said recess terminating in an annular runner lying in a plane normal to the shaft axis, the front face of the driver having a portion thereof abutting the end of the shaft; ears extended from the shaft through the driver and into the recess at the rear face thereof, said ears being bent over the bottom of the recess to hold the driver to the shaft, said recess in the rear face of the driver being deeper than the thickness of the ears so that no portion of said ears projects 3:. smooth sliding engagement therewith whereby RALPH W. MAGNUSEN.

eme? the end wall of the cover and the runner coact I IIIIIINCESOI'I'ED Thei'ollovingrdereneelareoirccordinthe iileoi'thispatent:

UNIT!) STATE PATENTS Number Name Date 2,358,991 L. W. Miller Sept. 28, 1944 2.437.166 I. 0. Indie Mar. 2. 1048 

